Secretary of State Lawrence S. Eagleburger, arriving for make-or-break arms control talks, said Sunday that there is "a better than 50-50 chance" that the United States and Russia will sign a treaty cutting nuclear arsenals by more than two-thirds before President Bush leaves office. Eagleburger negotiates today with Russian Foreign Minister Andrei A. Kozyrev and Defense Minister Pavel S.

For 48 hours, the two Russians and their Belarussian accomplice holed up in the dreary border town of Brest, waiting for two contacts from Poland to show up. To kill time and the autumn chill, the trio opened a bottle of vodka and began a round-the-clock drinking party. When the Poles arrived in the city of 238,000 in western Belarus, the Russians produced the lead capsule they had stolen from a top-secret installation 1,200 miles to the east. The Poles examined it.

The second Strategic Arms Reduction Treaty--which would cut nuclear weapons and which once was hailed by President Bush as a major achievement of his Administration's diplomacy--is unlikely to be completed by the time Bush leaves office because of Russian misgivings and American uncertainty, officials said this week. Russia has asked for several changes in the basic framework for a new agreement that Bush and Russian President Boris N. Yeltsin announced in June.

A flurry of arrests of Eastern European black marketeers trying to sell nuclear material in the West has raised alarm bells of a potential proliferation nightmare. In the wake of the Soviet Union's collapse, Western fears initially focused on Moscow's top atomic scientists and the need to prevent them from selling their skills to dictators, who could then engage in nuclear blackmail. So far, such brain-drain has not occurred, according to those monitoring the Soviet nuclear industry.

The Russian government has raised at least 22 substantive questions about a proposed treaty to destroy two-thirds of the U.S. and Russian nuclear arsenals, apparently frustrating President Bush's hope of completing the pact before Election Day, a senior Administration official said Thursday. Although the official said he is confident the treaty will be completed, the procedure he outlined could take weeks or months.

Nobody told the villagers why the fish in the river turned blind. Or why bulldozers showed up one day to plow under the road. So, they continued to cut hay in the meadows. When these peasants were forced by soldiers to leave their cottages in the Urals, they still didn't get a frank explanation. And even when they began to die, they were not told the truth. The history of the Soviet nuclear program is one of both great scientific prowess and vast human suffering.

It was about three years ago in this ramshackle Siberian farming and mink-breeding town that the Yellow Children began to appear. After hospital treatment, the jaundice that turns some newborns here a dull yellow eventually disappears. But it is not their only problem, for these infants also show signs of congenital defects in their nervous system and organs. They begin to walk later than other children, are oddly silent and have a vocabulary that remains infantile far too long, doctors say.

Not until Tuesday morning in the quiet of the Oval Office was it clear that an agreement was in hand. And, in the end, it was Boris N. Yeltsin himself who swept away the final logjam with a single emphatic sentence. In the final decision of a five-month-long negotiating sprint, the Russian president discarded decades of Soviet arms control doctrine and agreed to a nuclear arms pact that could leave his country holding fewer atomic warheads than the United States.

The sweeping U.S.-Russian arms pact announced Tuesday is far more than just another after-the-fact acknowledgment that the Cold War is over. It means that, for the first time in a generation, neither Americans nor Russians will have reason to live in fear of a sudden, preemptive nuclear attack by the other.